Millennial movers have hastened the growth of left-leaning metros in southern red states such as Texas, Arizona, and Georgia. It could be the biggest political story of the 2020s.

Liberals in America have a density problem. Across the country, Democrats dominate in cities, racking up excessive margins in urban cores while narrowly losing in suburban districts and sparser states. Because of their uneven distribution of votes, the party consistently loses federal elections despite winning the popular vote.

The most famous case was in 2016, when Hillary Clinton lost the election despite her 2.4-million-vote margin. Clinton carried Manhattan and Brooklyn by approximately 1 million ballots—more than Donald Trump’s margins of victory in the states of Florida, Arizona, Georgia, North Carolina, Michigan, Wisconsin, and Pennsylvania combined.

But 2016 wasn’t a fluke. Neither was 2000, when Al Gore lost the election despite winning 500,000 more votes. A recent paper from researchers at the University of Texas at Austin concluded that Republicans are expected to win 65 percent of presidential contests in which they narrowly lose the popular vote.

Democrats can blame the Electoral College for these losses—as they should. But according to the Stanford political scientist Jonathan Rodden’s new book, Why Cities Lose, it’s not just the districting. It’s the density. All over the world, liberal, college-educated voters pack into cities, where they dilute their own voting power through excessive concentration. “Underrepresentation of the urban left in national legislatures and governments has been a basic feature of all industrialized countries that use winner-take-all elections,” he writes.

So just imagine what would happen to the American political picture if more Democrats moved out of their excessively liberal enclaves to redistribute themselves more evenly across the vast expanse of Red America?

Or don’t imagine. Just … wait.

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Two weeks ago, I published an article on what I called the urban exodus. More specifically, it is a blue urban exodus, as left-leaning metros in blue states are losing population. The New York City metro area is shrinking by 277 people every day. Other areas bleeding thousands of net movers each year include Los Angeles, San Francisco, San Jose, San Diego, Chicago, Boston, and Baltimore—all in states that routinely vote for Democrats by wide margins.

These movers are U-Hauling to ruddier states in the South and West. The five fastest-growing metros of the past few years—Dallas, Phoenix, Houston, Atlanta, and Orlando, Florida—are in states won by Trump. The other metro areas with a population of at least 1 million that grew by at least 1.5 percent last year were Las Vegas; Austin, Texas; Orlando, Florida; Raleigh, North Carolina; Jacksonville, Florida; Charlotte, North Carolina; San Antonio; Tampa, Florida; and Nashville, Tennessee. All of those metros are in red or purple states.

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It’s not just liberals moving to the South. After all, movers to Florida are often retirees who fit squarely in the Fox News demo, and some of the people moving from California to Texas are conservatives. But today’s domestic migrants are often college graduates of the exceeding liberal Generations Y and Z. “The current migration to these suburbs is mostly people in their 20s and 30s, or Millennials, who are more diverse and liberal than the rest of the population,” said William Frey, a demographer at the Brookings Institution. According to his research, Americans ages 20 to 40 are three times as likely to move as people ages 50 to 70.

William Frey analysis of census data

This drip-drip-drip of young residents trickling down into red-state suburbs is helping to turn southern metros into Democratic strongholds. (Of course, migration isn’t the only factor pushing these metros leftward, but more on that later.) In Texas, Democrats’ advantage in the five counties representing Houston, Dallas–Fort Worth, San Antonio, and Austin (the “Texas Five” in the graph below) grew from 130,000 in the 2012 presidential election to nearly 800,000 in the 2018 Senate election.

In Arizona, from 2012 to 2016, Democrats narrowed their deficit in Maricopa County, which includes Phoenix, by 100,000 votes. Two years later, in the 2018 Senate election, the county swung Democratic, with Democrats gaining another 100,000 net votes.

In Georgia, from the 2012 presidential election to the 2018 gubernatorial elections, the four counties comprising most of Atlanta and its suburbs—Fulton, DeKalb, Cobb, and Gwinnett—increased their Democratic margin by more than 250,000.

Source: U.S. Census Bureau

What’s remarkable about these changes isn’t just their size, but their resemblance to Trump’s 2016 margins. Trump won Texas in 2016 by 800,000 votes. He won Arizona by 90,000 votes. He won Georgia by 170,000 votes. If these states’ biggest metros continue to move left at the same rate, there is every reason to believe that Texas, Arizona, and Georgia could be toss-ups quite soon.

As noted above, migration isn’t the only reason southern metros might be shifting to the Democratic Party: Longtime residents may be switching parties in response to Trump, for instance. Republicans have likely hurt themselves by moving further to the right to galvanize their white exurban and rural base, even as their support has thinned in the suburbs and among working-class white women.

But domestic migration is key. Just look at Texas. CNN exit polls for its 2018 Senate election showed that Beto O’Rourke was buoyed by recent movers, winning more than 60 percent of those who had moved to Texas within the past 10 years. At current migration rates, the “Texas Five” counties could easily add another 200,000 votes between 2016 and 2020, putting more pressure on Trump’s margin in the state. A September poll conducted by Univision and the University of Houston found the top six Democratic presidential contenders all leading Trump in Texas.

Outside of national elections, the blue flood of the sunbelt could have other political implications, like more showdowns between blue cities and red states. As The Atlantic’s David Graham has argued, North Carolina's GOP-led general assembly has waged war against liberal cities like Charlotte, for instance by reversing a local ordinance that banned discrimination against LGBT people. This sort of state-city showdown could become a regular feature of southern politics. In the last six months, both the Dallas Morning News and the Dallas Observer have run features bemoaning the Californication of northern Texas, with the former noting that “conservatives fear these domestic migrants will bring with them a liberal ideology that would disturb the Texas way of living.”

While such confrontations may be inevitable, over time the growth of liberal metros could force the Republican Party, which has lately been living off the fumes of retrograde xenophobia, to compete more aggressively for votes in the New South—that is, to be a party for moderates, black voters, and immigrants. The political shift could swing the other way, too: Democratic transplants to Dallas and Houston could edge right toward Republican territory, won over by their conservative neighbors’ arguments for lower levels of state and local taxation.

Overall, the southern suburbanization of Democratic votes could be a force for good, not only for Democrats but also, perhaps, for the future GOP—and, therefore, for the country at large. Without changes to the Electoral College or to the distribution of Democratic votes, the U.S. may be doomed to replay the 2016 election for several more cycles. Coastal liberals will remain justifiably furious that their votes are systematically discounted, while rural conservatives will remain justifiably indignant that the heart of American business and media has flocked to cities that regard the countryside as a xenophobic backwater. The southern blue flood is not a cure-all for this schism. But if more white rural families join liberal transplants and non-white families in America’s diverse southern suburbs, Americans might discover, through the sheer fact of neighborly proximity, a less vitriolic and more optimistic political future.